1. Field of the Invention
The invention relates to combustion chamber systems for positive-displacement spark-ignited internal combustion engines and to displacement-type scavenging and charging systems for the purpose of replacing fuel/air mixes in the combustion chamber.
2. Description of Related Art
Positive-displacement spark-ignited internal combustion engines benefit by limiting the period of time between a spark ignition and a peak pressure obtained from burning fuel. In crankshaft-type engines, rapid combustion assures that more of the fuel can be burned after the top-dead-center piston position, resulting in additional horsepower and more efficient consumption of fuel. In linear engines, such as may be used for fastening tools, rapid combustion allows for faster operation of the tools and less of a lag between the operator pulling a trigger and the fastener being driven. Shorter combustion times also prevent pre-expansions of the combustion chamber such as by early movement of a power piston until combustion pressures reach higher magnitudes. As a result, higher velocities can be communicated to the power piston for driving fasteners.
One way of achieving the higher burn rates is to induce turbulence of the fuel-air mixture in the combustion chamber. Such turbulence is known to shorten ignition-to-peak-pressure time while boosting peak pressures. A fan or other moving element can be located within combustion chambers to induce turbulence prior to ignition.
Higher peak combustion pressure from a given amount of fuel at a given compression can also be obtained by dividing the combustion chamber into a pre-combustion chamber and a main combustion chamber that are ignited in sequence. A spark igniter located at one end of the pre-combustion chamber remote from the main combustion chamber ignites a fuel-air mix in the pre-combustion chamber. A flame front ignited at the remote end of the pre-combustion chamber propagates toward the main combustion chamber, pushing a mixture of fuel and air into the main combustion chamber in advance of its arrival. Both turbulence and increased pressure are created in the fuel-air mixture of the main combustion chamber, which is ignited upon arrival of the flame front from the pre-combustion chamber.
My U.S. Pat. No. 6,840,033 for a Combustion Chamber System discloses various configurations of a pre-combustion chamber, including curved pre-combustion chambers that are believed to increase flame-front speed and to shorten ignition-to-peak-pressure time with respect to straight pre-combustion chambers of the same cross-sectional dimension. The peak combustion pressure is affected by the volume of the fuel-air mix in the combustion chamber. Adding to the length of the pre-combustion chamber can increase this volume. However, the added length can increase the ignition-to-peak-pressure time. In other words, if the flame fronts are required to traverse greater lengths, more time is required. In some designs, it was taking up to fourteen milliseconds at atmospheric pressure to obtain peak pressure.
Combustion efficiency is also dependent upon the quality of charge (i.e., fuel/air mix) in the combustion chamber. Between each firing, exhaust gases must be removed from the combustion chamber and a fresh charge introduced into the combustion chamber. To more completely remove the exhaust gases, it is preferable for the exhaust gases be mechanically displaced from the combustion chamber by reducing the volume of the combustion chamber to substantially zero prior to the introduction of a fresh charge.
U.S. Pat. No. 4,377,991 to Liesse entitled Internal Combustion Apparatus discloses the use of a plunger within the combustion chamber, which functions to expel unwanted exhaust gases at one side of the plunger while drawing in a fresh charge on the other. When released under a spring force, the fresh charge is transferred from one side of the plunger to the other through passageways that create turbulence. On one side of the plunger is a pre-mixing chamber, and on the other side of the plunger is the combustion chamber. Movement of the plunger in a direction that collapses the combustion chamber positively displaces exhaust gases from the combustion chamber while drawing fresh air and fuel into the expanding pre-mixing chamber. Movement of the plunger in the opposite direction transfers the fresh charge from the collapsing pre-mixing chamber into the expanding combustion chamber. The plunger is manually activated by depressing a push button.